1. Field of the Invention
The invention generally relates to using C3 to C14 aliphatic aldehydes and ketones, and C3 to C7 aliphatic primary and secondary alcohols to inhibit sprouting when applied to potato tubers.
2. Background of the Invention
Following harvest, potato tubers undergo a natural period of dormancy during which sprout growth is inhibited by endogenous hormones. As tubers emerge from dormancy and begin to sprout, respiration increases, starch is catabolized to sugars, and weight loss increases. The result is a decrease in quality of tubers destined for fresh and processing markets. Hence, inhibition of sprouting through chemical or physical means preserves quality and prolongs the duration of storage.
The sprout inhibitors registered for use on potatoes in the United States are CIPC (also known as chlorpropham, Sprout Nip®, etc.), maleic hydrazide (MH), DMN (also known as dimethylnaphthalene, 1,4SIGHT®, 1,4SEED®, 1,4SHIP®), DIPN (diisopropylnaphthalene, Amplify®), and clove oil (Biox-C®; Sprout Torch™). Except for MH, which is applied pre-harvest to actively growing plants, all inhibitors are applied post harvest when tubers are in the storage bin.
CIPC is the most effective and most widely used potato sprout inhibitor. The chemical is most often applied as a thermal aerosol fog into potato storages after wound-healing and prior to sprouting. In the Pacific Northwest, this is usually in November or December, before dormancy has ended. The chemical is fogged into storage at the recommended rate of 1 lb chlorpropham/600 cwt. One gallon of CIPC aerosol grade will treat 4200 cwt (210 tons) of potatoes. CIPC can inhibit sprouting and extend the storage life of table-stock and processing potatoes for up to 1 year with two applications.
CIPC is an effective sprout suppressant that has been used in the potato industry for about 40 years and the EPA considers it as a group E chemical (non-carcinogenic). CIPC was originally registered in the United States as a pre- and post-emergence herbicide in 1962 and the EPA has set residue limits for potato tubers. Notwithstanding its safety record, the trend today is to reduce the use of synthetic pesticides in agriculture in order to reduce residues in the world's food supply. The chemical is continually being scrutinized by the EPA as it is among the three pesticides found in the highest concentrations in the average American diet (Gartrell, M. J., J. C. Craun, D. S. Podrebarac, and E. L. Gunderson. 1986. Pesticides, selected elements, and other chemicals in adult total diet samples October 1980-March 1982. J. Assoc. Off. Anal. Chem. 69:146-161). CIPC constitutes over 90% of the total synthetic residues found in U.S. potatoes (Gartrell et al., 1986). The EPA recently issued a re-registration eligibility decision for CIPC and dropped the tolerance level for residues on potatoes. The economic importance of this chemical as a sprout inhibitor to the potato industry is illustrated by the fact that the registrants spent over $6,000,000 in this re-registration process. While other potential sprout suppressants have been identified (e.g. aromatic aldehydes and alcohols, methylesters of rape oil, carvone, jasmonates, spearmint and peppermint oils), none appear as effective as CIPC. A need thus exists to identify and develop the most benign chemicals possible (ideally natural, phytochemicals) that are effective as sprout inhibitors.
1,4SIGHT® (94.7% DMN=1,4-dimethylnaphthalene) is one such natural chemical that is also registered for sprout control, but it tends to be less effective than CIPC. DMN is naturally produced in potatoes. It is more volatile than CIPC and thus dissipates from tubers more rapidly than CIPC. Multiple applications of DMN are required to maintain season-long sprout inhibition. DMN is vaporized and applied as an aerosol into bulk storages. It can be applied any time after tubers are placed in the bin but is usually applied later in the fall or early winter when sprouting potential begins to increase. DMN is registered for use at a rate of 1 lb DMN/500 cwt (=20 ppm on a DMN to potato weight basis). Because of the need for multiple applications of DMN to achieve prolonged inhibition of sprouting, DMN is more costly to use than CIPC.
Other natural volatile sprout inhibitors have been identified. Carvone (derived from caraway seed) is commercially available for use on potatoes in the Netherlands (Hartmans, K. J., P. Diepenhorst, W. Bakker and L. G. M. Gorris. 1995. The use of carvone in agriculture—sprout suppression of potatoes and antifungal activity against potato-tuber and other plant-diseases. Industrial Crops and Products 4:3-13). The following US patents describe the use of various compounds for the inhibition of potato sprout formation: U.S. Pat. No. 5,436,226 to Lulai, et al. (Jul. 25, 1995) describes the use of jasmonates; U.S. Pat. No. 5,580,596 to Winkelmann et al. (Dec. 3, 1996) describes the use of rape oil and certain long-chain alcohols, either alone or in combination; U.S. Pat. No. 5,139,562 to Vaughn et al., (Aug. 16, 1992) describes the use of volatile monoterpenes (e.g. from eucalyptus, peppermint, spearmint, etc.); and U.S. Pat. No. 5,129,951 to Vaughn et al., (Jul. 14, 1992) describes the use of aromatic aldehydes and alcohols. In addition, Vokou et al. (1993) have demonstrated that the essential oils from a multitude of herbs (e.g. sage and rosemary) possess sprout inhibiting activity in potatoes.
There remains an ongoing need to provide alternative sprout inhibitors that are safe and effective, particularly sprout inhibitors that are natural compounds, and that do not pose a threat to the environment or to the health of humans and other species.